Process for condensing hydrogenous chlorine gas



Unite The present invention relates to a process for the condensation of hydrogeneous chlorine gas.

The high requirements today demanded of chlorine in further processing call for a development of processes which enable chlorine gas to be condensed practically quantitatively and the maximum yield to be obtained in liquid form.

The same holds true for the case where only part of the chlorine undergoes condensation but where there is no use for the inferior quality chlorine residue of the condensation.

Cell chlorine from plants which decompose aqueous solutions of alkali metal chlorides contains always certain amounts of CO H and N The gases, which are uncondensable under the pressure and temperature conditions of the chlorine condensation, appear in cell chlorine in a proportion of l2% dependent on the process applied and the operating conditions in modern plants, but the proportion of these gases in cell chlorine may be considerably greater when the process used is disturbed or when the plants are in poor condition. When, for example, the gas used as starting material has been produced electrolytically by the mercury process, it is found in a 90% condensation that the residual gas normally contains already about 4% of H which is said to be the tolerable upper limit for a nonexplosive character of the escaping gas mixture.

A process has already been described in the pertinent literature (ind. & Eng. Chem., September 1953, page 1832) wherein a 98.5% condensation is reached in that the compression is carried out in two stages and liquefaction is brought about by cooling; in this process the escaping gases are diluted with air following each stage to be below the explosion limit.

This known process involves, however, the disadvantage that stronger load variations imply a constant control of the amount of air introduced in order to prevent too strong or too low an air dilution and accordingly a deterioration of the condensation degree in the second stage, or the evolution of explosive gas mixtures.

A further disadvantage of the known process resides in the fact that it is carried out under a relatively high pressure, for example under a pressure of 1.26 atmospheres gauge in the first stage and under a pressure of 3.85 atmospheres gauge in the second stage of the process, and an error in dosing the air gives rise easily to an ignition of the gas mixture in the second stage.

The known process is further complicated in that the air must be carefully dried prior to being used for dilution.

Processes are also known which are carried out in the absence of preventive measures whatsoever against the evolution of highly explosive residual gases. The risks involved in these processes, i.e. that walls of iron containers, conduits or fittings may burn ofi in the chlorine current following the ignition at a temperature slightly above 100 C., are well known in the art.

We have found that the aforesaid disadvantages can be avoided and that hydrogeneous chlorine gas can be liquefied almost quantitatively without the danger of explosion by liquefying more than 99.5% of the chlorine tates Patent 0 M gas, that is 1% more than in the known process referred to above.

In carrying out the process of this invention chlorine gas is forced into a coolingdevice by means of a conveyor, wherein the condensation is carried out in various stages, preferably in two stages, provided the chlorine gas is condensed in the first stage or first stages by means of a cooler of known design so that the evolution of explosive residual gas is avoided and provided that the chlorine is condensed in the second or following cooling stages, for example to an extent of more than 99.5 to evolve explosive residual gas, the latter stages being so designed that the gas is distributed into smallest spaces for condensation.

The following statements are made to illustrate the invention.

Chlorine is compressed in one stage and cooled in at least two stages, the pressure and temperature applied being so selected that the chlorine is condensed in the first cooling stage or cooling stages to evolve a residual gas the hydrogen content of which is below the explosion limit, that is below 4%.

In the second stage or the following stages, the chlorine is cooled to so low a temperature that more than 99.5% of the chlorine used is liquefied. The residual gas evolved has an explosive character. In order to prevent the expansion of an explosion wave in the case of an ignition, if an, the gas chambers are so narrowly designed that at a local ignition the dissipation of the heat evolved takes place so rapidly that the explosion wave cannot expand. In order to prevent explosive gas mixture from diffusing into the larger spaces of the first cooling stage in the event the production is interrupted, nonreturn valves of suitable design are inserted between the first and second stages or the following stages which contain nonexplosive and explosive residual gas.

The coolers used in the second stage or the stages with explosive residual gas may be of various types. There may be employed, for example, a bundle of very narrow tubes or narrow annular spaces may be formed in more spacious tubes by means of replacement bodies. The cooling spaces may be filled with bodies which are in a good heat-conducting contact with the cooled walls and distribute the gas to be condensed into small units of volume.

In order to prevent that the heat transmission is handicapped, it is advantageous to very carefully purify the chlorine to be treated. In accordance with todays drying technique with sulfuric acid, the purifying apparatus is shifted towards the side of dry chlorine. In this case, purification may be brought about by means of a mechanical or electrostatic filter. When the chlorine is dried in known manner by cooling the moist chlorine gas to a temperature which, advantageously, is below 0 C. in the presence of hydrogen chloride, then it is suitable to purify the chlorine electrostatically.

In order to avoid the ignition, all apparatus parts are grounded so that differences in potential, for example owing to static electricity, which may involve spark formation cannot occur.

The following example serves to illustrate the invention, but it is not intended to limit it thereto:

Example Chlor ne from a mercury cell plant of the following composition 98.8 percent by volume of chlorine 0.6 percent by volume of CO 0.4 percent by volume of H 0.2 percent by volume of N +O was compressed to a total pressure of 2.5 atmospheres absolute. The first stage was cooled to a temperature of Patented July 10, 1962 20 6.; about 90% of The residual gas had the following composition:

89.35 percent of chlorine 3.55 percent H 5.33 percent C 1.78 percent N +O 7.69 percent of chlorine 30.77 percent H;

46.16 percent CO 15.39 percent N +O We claiin:

l. A process for condensing hydrogen-containing chlorine gas which comprises cooling said gas in a first stage, while under superatmospheric pressure, to a temperature the chlorine was liquefied.

sufficient to condense a proportion of the chlorine therein that is insufiicient to leave an uncondensed residual gas containing an explosive proportion of hydrogen, 'and further cooling said residual gas in a second stage for condensing additional chlorine and thereby forming a second stage residual gas containing an explosive proper tion of hydrogen, said second stage comprising a plurality of small cooling zones capable of confining and rapidly dissipating the heat of any small local explosions of said second stage residual gas.

2.'A process as defined in claim 1 wherein the first and second stage cooling steps are carried out at a pres sure of approximately 2.5 atmospheres.

3. A process as defined in claim 1 wherein the proportion of chlorine condensed in the first stage is approximately 90% of the chlorine" contained in the initial hydrogen-containing gas.

4. A process as defined in claim 1 wherein the proportion of chlorine condensed in the first stage is approximately 90% of the chlorine contained in the initial hydrogen-containinggas and the proportion of total chlorine condensed in the first and second stages is in excess of 99.5% of the chlorine contained in the initial hydrogencontaining gas. i

5. A process as defined in claim 1 wherein the first and second stage cooling steps are carried out at a pressure of approximately 2.5 atmospheres, the initial gas is cooled to a temperature of about 20 C. in the first stage and to a temperature'of about C. in the second stage.

References Cited in the file of this patent UNITED STATES PATENTS 2,556,850. Ogorzaly L June 12, 1951 2,754,666 Sp itzer July 17; 1956 OTHER REFERENCES Sanders et al.: Mercury Cell Chlorine and Caustic, Industrial and Engineering Chemistry, volume 45, number 9, September 2, 1953, published by American Chemical Society, Easton, Pennsylvania, page 183 relied on. 

1. A PROCESS FOR CONDENSING HYDROGEN-CONTAINING CHLORINE GAS WHICH COMPRISES COOLING SAID GAS IN A FIRST STAGE, WHILE UNDER SUPERATMOSPHERIC PRESSURE, TO A TEMPERATURE SUFFICIENT TO CONDENSE A PROPORTION OF THE CHLORINE THEREIN THAT IS INUSUFFICIENT TO LEAVE AN UNCONDENSED RESIDUAL GAS CONTAINING AN EXPLOSIVE PROPORTION OF HYDROGEN, AND FURTHER COOLING SAID RESIDUAL GAS IN A SECOND STAGE FOR CONDENSING ADDITIONAL CHLORINE AND THEREBT FORMING A SECOND STAGE RESIDUAL GAS CONTAINING AN EXPLOSIVE PROPORTION OF HYDROGEN, SAID SECOND STAGE COMPRISING A PLURALITY OF SMALL COOLING ZONES CAPABLE OF CONFINING AND RAPIDLY DISSIPATING THE HEAT OF ANY SMALL LOCAL EXPLOSIONS OF SAID SECOND STAGE RESIDUAL GAS. 